Process for the manufacture of aromatic amino-oxy-compounds.



A. PIGUETM E. SfEmeum-a & e. STOCKER.

PROCESS FOR THE MANUFACTURE OF AROMATIC AMINO-OXY-COMPOUNDS. APPLICATION FILED ocT. 27; 1916.

1 ,%3,@%@ o r V Patented Sept. 11, 1917.

"UNI AB ANT Wren ALFRED PIG'UET, EWAIJD STEIN BUGH, AND ROBERT STOCKER, OF BASEL, SWITZER- LAND, ASSIG-NORS TO SOCIETY OF CHEMICAL INDUSTRY IN BASLE, 0F BASEL,

SWITZERLAND.

PROCESS FOR THE MANUFACTURE OF AROMATIC AMINO-OXY-COMPOUNDS.

Specification of Letters Patent. I

Patented Bept. Jlil, 1191?,

Application filed October 27, 1916. Serial No. 128,009.

To all whom it may concern:

Be it known 'that we, Dr. ALFRED PIGUET, Dr. EWALD STEINBUQH, and Dr. ROBERT SrooKER, all three citizens of the Swiss Republic, and residents of Basel, Switzerland, have invented a new and useful Process for the Manufacture of Aromatic Ammo-Oxy- Comp0unds, of which the following is a full, clear, and exact specification.

By the electrolytic reduction of an aromatic nitrocompound in an acid electrolyte two principal products are obtained in varying quantities i. e. the corresponding amin and the corresponding amino oxy com pound. For instance the reduction of nitrobenzene in sulfuric acid conduces to anilin and 1 4 amino oxy benzene (paraamidophenol) according to the formulae:

By using a tin, chromium or lead cathode, or an indifierent cathode in presence in the cathode chamber of tin chromium or lead or of the corresponding .metal-compound,

Buchner (U. S. A. Patents No. 700670, 736205, 761284) attains a pretty uniform reduction to amin, also in commercial working. On the other hand it has not been possible to reduce on a large scale the nitrocompounds to the correspondin amino-oxycompounds (by the methods itherto' employed).

In the manufacture of aromatic amino oxy-compounds by electrolytic reduction of nitro-compounds in presence of sulfuric acid of various strengths, cathodes of carbon or of a noble metal, such as platinum or silver have been used hitherto. Cathodes of nickel have also been recommended but have not been adopted in commercial working. The use of other common metals appears to be excluded since they conduce to the formation of amino-compounds in preponderating proportion. I

In the case of cathodes of a number of common metals, when the surface Jof the metal is clean, that is to say polished, the production of the amino-compound is diminished in comparison with that of the amino-oXy-compound; but after the oathodes have been in use for some time-their surfaces become changed and the formation of the aminocompound continually increases. The attempt might be made to keep the metal surface polished, but this is scarcely practicable. The said change ,of the cathode surface is due to the fact that, particularly in presence of a nitro-compound, some of the cathode metal dissolves in the electrolyte and in the course of the electrolysis is deposited on the cathode surface in a form which especially favors the formation of amino-compounds. Such deposition, therefore, is intentionally produced by Buchner to carry the reduction nearly completely to amino-compound, by using an indifferent electrode and adding a salt of copper, iron, chromium, lead or mercury, or the corresponding finely subdivided metal to the electrolyte.

We have discovered that, if there are at least two metals present in such a deposit on the cathode, the reduction tends to cease when the amino-oXy-compound has been formed.

By the present invention, therefore, the formation of amino-oxy-compounds is favored by conducting the electrolysis in the presence of two or more metals, which by continuously passing into solution and depositing on the surface of the cathode maintain the latter more or less coated with a deposit of two or more metals. When a cathode of a common metal is used this may supply one of the metals in the manner indicated above; the other may be added either as such or in the form of a salt. When an indifferent cathode is used at least two metals must be added to the electrolyte, each as such or as a salt.

By the present invention the formation of amino-oXy-compounds is consequently favored if two or more suitably selected metals are present at the same time in the cathode chamber. For instance, when nitrobenzene is reduced in dilute sulfuric acid with a. lead cathode, para-aminophenol and anilin are produced in the proportion 100 150, and if then in the same apparatus with the same lead cathode there is added to the cathode chamber some powdered bismuth, the anilin content of the product of the next electrolytic reduction falls to about 20 per cent. of the aminophenol. In succeeding operations the proportion is at first approximately the same and then gradually varies unfavorably to the aminophenol because every time the apparatus is emptied there is a loss of bismuth dissolved or suspended in v the electrolyte. the favorable lished.

The effect of the presence of more than one metal in hindering the formation of amino-compound and favorin that of amino-oxy-compound is not limited to the aforesaid lead-bismuth combination. The cathode may be of any suitable material and the metal or metals adapted for the case in point may be added. Thus we have used a large number of other metals, for instance arsenic, antimony, copper, nickel, tin, mercury and by combining them, as for instance copper with mercury, lead with arsenic, copper with tin and arsenic, so that they deposit on the cathode as required, we have obtained alwaysthe same or similar effects.

By adding more bismuth proportion is again estab- If the cathode is an indifie'rent material,

like carbon, the presence of suitable metals, such as copper and lead, has the advantage that no adherent coating of resin is produced on'the cathode. As already stated the metals may be added in the form of their salts; for-instance when using a lead cathode, copper sulfate may be added.

In the German Patent'No. 252759 it has already been proposed that lead containing a small proportion of copper should be used as electrode material, butthese electrodes are not suitable for the purpose in question when the working is continuous, apparently because at each successive operation the cathode surface becomes poorer in copper until finally the surface consists merely of lead-sponge, whereupon the reduction is completely to the amino-compound.

The cathode for producton of amino-oxycompounds may, however, be made of metals alloyed together instead of using one metal as cathode and adding another as an auxiliary, provided that the metals to be alloyed are so selected that even in continuous application of the cathode the proportion between the metals present on the cathode surface is not essentially altered, a condition not'existing, as already stated, in the lead-copper alloy previously suggested.

Besides the advantage that one is not restricted in the choice of the electrode material, the invention has the further important advantage that there need not be present in the electrolyte in the cathodechamber much more acid than will be combined at the end of the reduction with the base produced, and this limitation of the acid does not affect unfavorably the yield of the amino-oxy-compound. The consumption of acid is there ore the smallest possible, whereas according to former tenets the formation of amino-oxy-compound has been the better, the more concentrated the acid used as electrolyte.-

The following examples illustrate the invention, the accompanying drawing showing in a vertical section one of the many forms of apparatus which may be employed:

Example 1: The electrolytic vessel is a lead cylinder 1 which serves as anode. In it is placed a porous cylinder 2 containing -a copper cathode 3 in the form of a hollow perforated cylinder.

Within the cathode cylinder isa suitable stirrer 4. Into the cathode chamber extend one or more rods of lead 5. The anode chamber is charged with sulfuric acid of 30 per cent. strength, and

the cathode chamber with 25 liters of sulfuric acid of 15 Baum specific gravity and 6 kilos of nitrobenzene. By lively stir. ring the nitrobenzene is kept in emulsion in the sulfuric acid. The electrolysis is conducted at a temperature of 80-95 C. with a current of about 3 amperes per sq. dcm. of cathode surface at 3-3 l volts, until all nitrobenzene' has disappeared. The bases are liberated from the mass by adding milk of lime and the anilin formed as a by-prodnot is distilled. The remaining hot solution of para-aminophenol is filtered from calcium sulfate and evaporated to crystallization. .There is thus obtained pure paraamino-phenol in yield of about 50 per cent. of the weight of the nitrobenzene used, and as by-product anilin in a proportion of about 20 per cent. of the weight of the paraaminophenol simultaneously obtained. If arsenic is present as well as the copper and lead, such as is the case if arsenical sulfuric acid is used as the electrolyte, the. content of anilin will fall to 10-15 per cent. of the aminophenol. Instead of the arrangement described the cathode may be of lead and a copper rod may be suspended in the cathode chamber or some copper sulfate may be added to the chamber and renewed from time to time. 7

- Example 2: Instead of the co per cathode described in Example 1, a lead cathode is used and instead of the lead rods there are introduced into the cathode chamber about a manufacture of amino-oxy-compounds by electrolytic reduction of aromatic n1tro-com-- pounds in acid, which-jconsists in conducting the electrolysis in presence of at least two metals in the cathode chamber, which by continuously passing into solution and depositing on the surface of the cathode, maintain the latter always coated with a deposit of at least two metals.

2. The herein described process for the manufacture of amino-oxy-compounds by electrolytic reduction of aromatic nitrocompounds in acid, which consists in employing as electrolyte in the cathode chamber a diluted acid solution which contains not much more acid than is necessary to combine with the bases produced by the reduction.

3. The herein described process for the manufacture of amino-oxy-compounds by electrolytic. reduction of aromatic nitrocompounds in acid, which'consists in employing as electrolyte in the cathode chamber a diluted acid solution, which contains not much more acid than is necessary to combine with the bases produced by the reduction and in conducting the electrolysis in presence of at least two metals in the said cathode chamber, which by continuously passing into solution and depositing on the surface of the cathode, maintain the latter always coated with a deposit of at least two metals.

In witness whereof we have hereunto signed ournames this 6th day. of October 1916, in the presence of tWo subscribing witnesses.

' DR. ALFRED PIGUET.

DR. EWALD STEINBUCH. DR. ROBERT STOOKER. Witnesses:

ARNOLD ZUBER, ARMAND BITTER. 

